Rapid thermal process (RTP) has conventionally been known as a thermal processing method used in the manufacturing of semiconductor devices and the like (see, for example, Patent Document Nos. 1 and 2). An example of rapid thermal processing apparatus used in the RTP comprises a lamp for heating a substrate, a temperature sensor (e.g., pyrometer) arranged so as to oppose the lamp, and an edge ring for holding the substrate between the lamp and the temperature sensor. When the substrate inserted between the lamp and the temperature sensor is irradiated with infrared rays by using the lamp, the temperature of the substrate rises rapidly. The temperature sensor detects the heat radiated from the substrate.    Patent Document 1: Japanese Patent Publication No. 2711239    Patent Document 2: Japanese Translated International Patent Application Laid-Open No. 2002-510153